This invention relates to the measurement of the concentration of thyroid hormones in human serum and, more particularly, to radioimmunoassay for measurement of thyroxine (T.sub.4) in unextracted serum.
One known technique of radioimmunoassay for measurement of T.sub.4 in unextracted human serum employs a blocking agent, such as 8-anilino-1-naphthalene-sulfonic acid (ANS), to displace the T.sub.4 bound to thyroxine binding globulin (TBG) in the serum being assayed. A mixture of the blocking agent, a T.sub.4 binding antibody, radioactive T.sub.4 producing a known radioactive count, and buffering ions is added to a phalanx of as many as thirty test tubes containing respectively in duplicate the serum being assayed, a number of standard serums with different known concentrations of T.sub.4 for purposes of correlation, and a number of control pool serums. After an incubation period sufficient to allow the reaction of the T.sub.4 in the serum and the radioactive T.sub.4 with the antibody to proceed substantially to equilibrium, thereby producing antibody bound T.sub.4, a percentage of which is radioactive, polyethylene glycol (PEG) is added to the test tubes as a separating agent to precipitate the antibody bound T.sub.4. The precipitate in each test tube is removed from the supernatant, its radioactivity is counted, and the radioactivity count of the serum being assayed is correlated with the counts of the standard serums. Since reagents and serum are pipetted three times into a large number of test tubes in the described radioimmunoassay precedure, a substantial amount of laboratory time is expended and the risk of human error is relatively high.